Method of Determining Queried Fluid Cuts Along a Tubular

ABSTRACT

A method of identifying a queried fluid cut along a tubular includes, determining a first flow rate of a queried fluid flowing through all open zones, determining a flow rate of liquid through a selected zone, and closing the selected zone, determining a second flow rate of the queried fluid flowing through all open zones, and attributing a queried fluid cut to the selected zone as a percentage that the difference between the first flow rate of the queried fluid and the second flow rate of the queried fluid is of the flow rate of liquid through the selected zone.

BACKGROUND

Industries employ tubular systems for transporting multiphase fluids, such as, combinations of water and hydrocarbons, for example, from one location to another. Such systems commonly have multiple zones through which the multiphasic fluids enter the tubular. Each of the zones may produce an unknown amount of water as one of the constituents of the multiphasic fluids. A percentage of water that makes up a fluid flow is commonly referred to as the water cut. Systems and methods that allow operators to gain knowledge regarding the water cut attributable to each zone would be beneficial to operators.

BRIEF DESCRIPTION

Disclosed herein is a method of determining queried fluid cuts along a tubular. The method includes, determining a first flow rate of a queried fluid produced from a plurality of zones along the tubular, measuring a liquid flow rate produced by a selected zone of the plurality of zones, ceasing production from the selected zone, and determining a second flow rate of the queried fluid produced from the plurality of zones along the tubular minus the selected zone. Then determining a queried fluid cut of the selected zone as a percentage of the liquid flow rate produced by the selected zone that a loss between the first flow rate of the queried fluid and the second flow rate of the queried fluid represents.

Further disclosed herein is a method of determining queried fluid cuts along a tubular. The method includes, determining liquid produced by all zones along the tubular, determining a queried fluid cut of the liquid produced by all of the zones, calculating a queried fluid produced by all of the zones, determining liquid produced by a selected zone along the tubular, closing the selected zone, determining liquid produced by all zones except the selected zone, and determining a queried fluid cut of the liquid produced by all zones except the selected zone. And then calculating a queried fluid produced by all of the zones except the selected zone, and calculating the queried fluid cut for the selected zone as a difference in the queried fluid produced by all of the zones and the queried fluid produced by all of the zones except the selected zone and dividing by the liquid produced by the selected zone.

Further disclosed herein is a method of identifying a queried fluid cut along a tubular. The method includes, determining a first flow rate of a queried fluid flowing through all open zones, determining a flow rate of liquid through a selected zone, and closing the selected zone, determining a second flow rate of the queried fluid flowing through all open zones. And then attributing a queried fluid cut to the selected zone as a percentage that the difference between the first flow rate of the queried fluid and the second flow rate of the queried fluid is of the flow rate of liquid through the selected zone.

BRIEF DESCRIPTION OF THE DRAWINGS

The following descriptions should not be considered limiting in any way. With reference to the accompanying drawings, like elements are numbered alike:

FIG. 1 depicts a schematic view of a system for determining queried fluid cuts along a tubular disclosed herein; and

FIG. 2 depicts a partial flow chart of a method for determining a queried fluid cut of multiple zones along a tubular disclosed herein.

DETAILED DESCRIPTION

A detailed description of one or more embodiments of the disclosed apparatus and method are presented herein by way of exemplification and not limitation with reference to the Figures.

Referring to FIG. 1, a tubular system for determining a queried fluid cut at multiple zones along the tubular is illustrated generally at 10. Although the queried fluid could be any of multiple fluids that make up a multiphase fluid, water will be used as the queried fluid illustrated in embodiments disclosed herein. The tubular system 10 includes, a tubular 14 having a plurality of zones 16A-D distributed longitudinally along the tubular 14 and isolated from one another by seals 20, such as packers, for example. Each of the zones 16A-D have at least one port 18 through a wall 22 of the tubular 14, and at least one valve 26, configured to selectively variably occlude the port(s) 18 of the associated zone 16A-D. The system 10 also includes, a flow rate measuring device 30 configured to measure a total liquid flow rate, Q_(liq), flowing through all open zones 16A-D, as well as flow measuring apparatuses 34 distributed along the tubular 14 for measuring flow rates at various points along the tubular 14 including one upstream and one downstream of each of the zones 16A-D. Additionally, a water cut meter 38 is configured to determine water cut,

${{Wcut} = \frac{Q_{wat}}{Q_{liq}}},$

or the percentage of the total liquid flow rate, Q_(liq), that is water, Q_(wat). Alternate embodiments are contemplated wherein water, oil and gas are separated at surface and their flow rates determined separately after which the water cut is determined.

The system 10 includes just one water cut meter 38 located downstream of all of the zones 16A-D. In the embodiment illustrated herein the system 10 is applied downhole in the hydrocarbon recovery industry in a wellbore 42 and the water cut meter 38 is located at surface 46. Normally for a multi-zone single well producer, water cut and phase flow rates are measurable at surface after oil-gas-water separation. Since the system 10 only has the one water cut meter 38 or measurement, the water cut at each zone 16A-D is not directly measurable. Methods disclosed herein, however, allow an operator to determine the water cut, Wcut, that occurs at each of the zones 16A-D.

Referring to FIG. 2, a flow chart 50 illustrates a plurality of steps disclosed herein that facilitate the determination of water cut from each zone 16A-D. The variables used include superscripts to identify the step in which the measurement is made and subscripts to identify the location where the measurement is made. The process starts at step 0 defined as all valves 26 being open and all zones 16A-D producing fluid. Downhole pressure and temperature information is used to adjust the measured rates in standard (pressure/temperature) condition or downhole in-situ pressure/temperature condition or mass-rate condition, as production fluid (especially for hydrocarbons) properties (i.e., volume, density, bubble point, solution gas-oil ratio, etc.) are highly impacted by the in-situ fluid pressure and temperature (Tarek Ahmed, Equations of State and PVT Analysis). Measurements are made of total liquid flow rate at the surface 46 at step 0, Q_(liq-S) ⁰; water cut of the total liquid flow rate at the surface 46 at step 0, Wcut_(S) ⁰; and liquid flow rate produced by one of the zones 16A at step 0, Q_(liq-A) ⁰ (zone A in this example). It should be noted that some values could be calculated from other measured values depending upon equipment utilized. For example, if multiphase flow meters are used at the surface 46 to separately measure flow rates of the different liquids, such as, the water flow rate at step 0, Q_(wat-S) ⁰, and the oil flow rate at step 0, Q_(oil-S) ⁰, for example, then the total liquid flow rate at the surface 46 at step 0, Q_(liq-S) ⁰, can be Calculated With Formula (1):

Q _(liq-S) ⁰ =Q _(oil-S) ⁰ +Q _(wat-S) ⁰.  (1)

Additionally the water cut of the total liquid flow rate at the surface 46 at step 0, Wcut_(S) ⁰ can be calculated with formula (2):

$\begin{matrix} {{Wcut}_{S}^{0} = {\frac{Q_{{wat} - S}^{0}}{Q_{{liq} - S}^{0}}.}} & (2) \end{matrix}$

After the above measurements are made the valve 26A that controls occlusion of the zone 16A (the zone being analyzed first), is closed defining step 1. Once closed and flows are stabilized measurements are made of total liquid flow rate at the surface 46 at step 1, Q_(liq-S) ¹; water cut of the total liquid flow rate at the surface 46 at step 1, Wcut_(S) ¹; the water flow rate at step 1, Q_(wat-S) ¹, and the oil flow rate at step 1, Q_(oil-S) ¹.

Values of the foregoing variables can be used in formula (3) to determine water cut of the liquid flow rate produced by zone A at step 0, Wcut_(A) ⁰, which also equals the water cut of the liquid flow rate produced by zone A at step 1, Wcut_(A) ¹ since the water cut produced by a zone has been found to be substantially constant regardless of the occlusion of the zone A.

$\begin{matrix} {{Wcut}_{A}^{0} = {{Wcut}_{A}^{1} = \frac{{Q_{{liq} - s}^{0}{Wcut}_{S}^{0}} - {\left( {Q_{{liq} - S}^{0} - Q_{{liq} - A}^{0}} \right){Wcut}_{S}^{1}}}{Q_{{liq} - A}^{0}}}} & (3) \end{matrix}$

This formula may be more easily understood when thought of as first determining the water flow rate produced by all of the zones at step 0, Q_(liq-S) ⁰Wcut_(S) ⁰, then subtracting the water flow rate produced by all of the zones except zone A step 1 (since zone A has been closed), (Q_(liq-S) ⁰−Q_(liq-A) ⁰)Wcut_(S) ¹, which equals the water flow rate produced by zone A alone, Q_(wat-A) ⁰. The water cut from zone A is then found by dividing this water flow rate produced by zone A by the total liquid produced by zone A, Q_(liq-A) ⁰, which is formula (2) for determining water cut rewritten here as formula (2′) for zone A specifically.

$\begin{matrix} {{Wcut}_{A}^{1} = \frac{Q_{{wat} - A}^{0}}{Q_{{liq} - A}^{0}}} & \left. \left( 2’ \right. \right) \end{matrix}$

Application notes regarding formula (3): Wcut_(S) ¹, is actually the combined water cut of the zones left open (i.e. by closing zone 16A, while leaving the other zones in their original, open, conditions). Another important assumption of formula (3) is to assume that the combined water cut of the zones left open (16B-D) remain the same regardless of whether zone 16A is open or closed. The closing of zone 16A has minimal affect on the wellbore annulus pressure profile, therefore, the zonal water rate change and its impact on the combined water cut, Wcut_(S) ¹, is negligible. If a measured annulus pressure near bottom of the wellbore 42 has changed significantly after closing the zone 16A, it is suggested to adjust a surface wellhead choke 44 (i.e. decreasing the wellhead choke) to get a similar annulus pressure near bottom of the wellbore 42 as before applying this method to estimate the water cut, Wcut_(A) ¹.

This method can also be used for conditions having a combined gas-liquid flow near bottom of the wellbore 42. However, to avoid too much PVT calibration (Tarek Ahmed, Equations of State and PVT Analysis) and increase the accuracy of this application, it is suggested to use this method with wellbore flowing pressure above oil bubble point. In this way, at downhole, production fluid is in liquid phase flow condition.

If the water cut produced by zone A is calculated to be either a negative number or has a value that is greater than 1 an error has occurred and the process should be repeated after adjusting any settings that may have contributed to or caused such error.

The foregoing process can be repeated until all of the zones 16A-D have been closed and water cuts attributed to each of the zones 16A-D has been established. Closing of the zones 16A-D in a sequential manner starting with the zone 16A nearest to the water cut meter 38, at the surface 46 in this embodiment, and moving one at a time toward the zone 16D, furthest from the surface 46, will assure that the flow measurements taken at the surface 46 are correctly attributed to all of the zones 16A-D remaining open and not to the next zone 16B-D in the sequence being closed.

While the invention has been described with reference to an exemplary embodiment or embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the claims. Also, in the drawings and the description, there have been disclosed exemplary embodiments of the invention and, although specific terms may have been employed, they are unless otherwise stated used in a generic and descriptive sense only and not for purposes of limitation, the scope of the invention therefore not being so limited. Moreover, the use of the terms first, second, etc. do not denote any order or importance, but rather the terms first, second, etc. are used to distinguish one element from another. Furthermore, the use of the terms a, an, etc. do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced item. 

1. A method of determining queried fluid cuts along a tubular comprising: determining a first flow rate of a queried fluid produced from a plurality of zones along the tubular; measuring a liquid flow rate produced by a selected zone of the plurality of zones; ceasing production from the selected zone; determining a second flow rate of the queried fluid produced from the plurality of zones along the tubular minus the selected zone; and determining a queried fluid cut of the selected zone as a percentage of the liquid flow rate produced by the selected zone that a loss between the first flow rate of the queried fluid and the second flow rate of the queried fluid represents.
 2. The method of determining queried fluid cuts along a tubular of claim 1, further comprising repeating the foregoing process until all of the plurality of zones have been closed and a queried fluid cut of each zone has been determined.
 3. The method of determining queried fluid cuts along a tubular of claim 1, further comprising closing the plurality of zones sequentially.
 4. The method of determining queried fluid cuts along a tubular of claim 3, wherein the closing sequentially starts with closing the zone nearest to a queried fluid cut measuring apparatus then continues with closing the zone next nearest to the queried fluid cut measuring apparatus and so on.
 5. The method of determining queried fluid cuts along a tubular of claim 1, further comprising ascribing values of queried fluid cuts that are greater than one and less than zero to errors requiring redoing at least a portion of the foregoing process.
 6. The method of determining queried fluid cuts along a tubular of claim 1, wherein the determining the first flow rate of the queried fluid produced from the plurality of zones along the tubular further comprises: measuring a first flow rate produced from the plurality of zones; measuring a first queried fluid cut of the first flow rate; and calculating the first flow rate of the queried fluid produced from the plurality of zones.
 7. The method of determining queried fluid cuts along a tubular of claim 1, wherein the determining the second flow rate of the queried fluid produced from the plurality of zones along the tubular minus the selected zone further comprises: measuring a second flow rate produced from the plurality of zones minus the selected zone; measuring a second queried fluid cut of the second flow rate; and calculating the second flow rate of the queried fluid produced from the plurality of zones minus the selected zone.
 8. The method of determining queried fluid cuts along a tubular of claim 1, wherein the queried fluid is water.
 9. A method of determining queried fluid cuts along a tubular comprising: determining liquid produced by all zones along the tubular; determining a queried fluid cut of the liquid produced by all of the zones; calculating a queried fluid produced by all of the zones; determining liquid produced by a selected zone along the tubular; closing the selected zone; determining liquid produced by all zones except the selected zone; determining a queried fluid cut of the liquid produced by all zones except the selected zone; calculating a queried fluid produced by all of the zones except the selected zone; and calculating the queried fluid cut for the selected zone as a difference in the queried fluid produced by all of the zones and the queried fluid produced by all of the zones except the selected zone and dividing by the liquid produced by the selected zone.
 10. The method of determining queried fluid cuts along a tubular of claim 9, further comprising repeating the foregoing steps until a queried fluid cut from each zone is determined.
 11. A method of identifying a queried fluid cut along a tubular, comprising: determining a first flow rate of a queried fluid flowing through all open zones; determining a flow rate of liquid through a selected zone; closing the selected zone; determining a second flow rate of the queried fluid flowing through all open zones; and attributing a queried fluid cut to the selected zone as a percentage that the difference between the first flow rate of the queried fluid and the second flow rate of the queried fluid is of the flow rate of liquid through the selected zone. 